Parallelepipedal cardboard boxes for packaging are known which include panels than can be folded over two by two and that are integral with the vertical faces of the box so as to form on the one hand the bottom of the box and on the other hand the top of this box. These boxes are commonly known in the art as American boxes. The invention is applicable to certain types of American box. The boxes that can be used with the invention generally have two lateral flaps which, when they are folded at an angle of 90.degree., are disposed opposite each other at the same level, and two flaps, one on the outside and the other on the inside, which, when they are folded at an angle of 90.degree., cover practically the whole of the opening of the box and are stuck to each other to form and close the box.
In order to open such conventional boxes, it is necessary to insert an instrument, for example the blade of a knife, under the flap or flaps, or to take hold of the latter by their lateral edge by hand or to put the box out of shape in order to be able to lift the flaps, all of which are common, but relatively inconvenient, operations. It has already been proposed to equip such cardboard boxes with tongues or tear-off strips made of plastic, such as polyethylene for example, enabling the cardboard to be torn and the box to be thus opened. However, the use of such tear-off strips embedded in the cardboard increases the cost of the box and prevents recycling because of this inclusion of a foreign material.
The invention therefore proposes to provide a box with an efficient means of opening, at a lower cost than that of boxes equipped with tear-off strips but which is easy to open and does not require the use of additional tools.